Lignans are phytoestrogens widely used in dietary supplements and functional foods. After oral
ingestion, these polyphenols are metabolized to enterolignans, the main gut microbiota-derived
metabolites with weak estrogenic/anti-estrogenic activities. The ABCG2 transporter is highly
expressed in the mammary gland and could be responsible for enterolignan accumulation. We
aimed here at evaluating the levels of enterolignans and their conjugates in plasma, milk and
mammary tissue from wild-type and knockout Abcg2-/- female mice after a lignan-enriched diet
for one week. In vitro transepithelial transport of enterolignans was also assayed with ABCG2-
transduced cells. Enterolactone and enterodiol levels were higher in plasma and lower in milk
from Abcg2-/- compared with wild-type mice. Both enterolactone and enterodiol were
accumulated in the mammary gland but with significant differences only for enterolactone. Our
results suggest that ABCG2 may be determinant for plasma and milk levels of enterolignans
whose accumulation could exert chemopreventive effects against breast cancer